[Xapian-discuss] Search performance issues and profiling/debugging

[Ron Kass]

Hi Chris

We prefer to work with Xen at the moment as in the future we will likely 
use Xapian over Xen anyway.

What you refer to as competing resources, might effect performance but 
not the variations in estimates. Also, the fact that the search is 
consistently slow in repeating searches for "no recip" but not for other 
searches, hints that it is not a Xen resource competing issue.
Again, the only thing that this machine is doing is this test. Dom0 does 
nothing. Its not stressed, its not using any resources at all.

Although we should never rule out something completely without checking, 
I believe quite strongly that the issues we are seeing are not coming 
from Xen, as per this instance it is a regular dedicated Linux (centos 
5) machine and the resources are fully dedicated to it.

Cheers,
Ron


Chris Good wrote:
> Ron Kass wrote:
>   
>> Not sure what you mean by "other VMs could well be confusing your results"
>> We use XenServer on this machine, but we have only one instance (DomU), 
>> and only this instance is running everything locally. So there are no 
>> other VMs to confuse things, and even if there were, they have nothing 
>> to do with the VM we run the test on or with the test itself.
>> (Can you clarify what you mean?)
>>     
>
> If you have multiple VMs sharing the same hardware then activity on one
> will obviously affect the performance on other VMs.  Since you're running
> a lone DomU other DomUs aren't going to be competing for resources but 
> it's possible that something in Dom0 is getting swapped in and running.
>
> How are you accessing your drives, is DomU accessing the raw devices or is
> it mapped via virtual files from Dom0?
>
> Is it possible to run these tests either directly from Dom0 or even better
> with a non-xen kernel?
>
> Given your current configuration of a single VM xen isn't adding anything 
> so removing it would eliminate any side-effects of it.  I also suspect
> that it would cure your oprofile issue.
>
> Chris
>
>
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